Field of the Invention
The present invention relates to sand boils and more particularly to techniques for controlling sand boils.
Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
A sand boil is an eruption of a liquefaction of sediment (e.g., sand) and water through a bed of sediment due, for instance, to differences in water pressure on two sides of a levee (or other water-retaining structure such as a dam) which causes liquefied sediment and water to flow from beneath the levee and out of a sand boil on the land side of the levee. If left unchecked, a sand boil can continue to grow in size, thereby decreasing the effectiveness of the levee in preventing water from reaching the land side. Moreover, an unchecked sand boil can result in internal erosion of the foundation soils underneath the levee that can create one or more channels or pipes through the levee embankment. The creation of channels and pipes can quickly pick up pace and eventually result in failure of the levee.
FIG. 1 is a cross-sectional side view of a typical sand boil 110 on the land side 120 of a nearby levee 130. As represented by the long curved arrows in FIG. 1, water from the water side 140 of the levee 130 percolates through the soil 150 under the levee and erupts out of the sand boil 110 as a liquefaction of sediment and water. Although not explicitly shown in FIG. 1, a sand boil typically has a substantially circular opening at ground level that can vary in diameter from pin-hole size to a few feet in diameter. Left unchecked, sand boils have been known to grow even larger.
A sand boil is difficult to stop. The most-common method for controlling an existing sand boil is to form a body of water above the boil to create enough pressure to slow or stop the flow of water through the boil. A sufficiently slow flow of water will slow movement of liquefied soil, thereby inhibiting or slowing significant erosion under a nearby levee. Such a body of water is most often created by surrounding the sand boil with a ring of stacked sandbags, such that the water level within the ring will rise, thereby increasing the underground hydrostatic pressure at the sand boil and decreasing the flow of water and sand out of the sand boil. Unfortunately, this method is labor intensive and costly, and the increased hydrostatic pressure in the ground near the sand boil can result in the formation of one or more new sand boils nearby.
Another conventional technique for forming a body of water above a sand boil is to place an open-ended barrel over the boil. The seeping water will fill up at least a portion of the barrel, thereby creating the body of water above the boil. Here, too, as in the case of a ring of sand bags, although the body of water may slow the flow of liquefied sediment through the existing sand boil, the increased underground hydrostatic pressure can result in the formation of new, nearby sand boils.
Another known technique for controlling sand boils is to dump large amounts of material such as sand and gravel over the entire area impacted by existing sand boils and threatened by new sand boils. This typically involves the labor intensive, expensive, and time consuming use of dump trucks to bring the material from a remote storage location to the site and bull dozers to distribute the material over the relevant area.